(Reuters) - U.S. health regulators will add warnings to the labels of widely used cholesterol lowering drugs, such as Lipitor, to indicate that they may raise levels of blood sugar and could cause memory loss.

The Food and Drug administration announced the changes to the safety information on the labels of statins such as Pfizer Inc's Lipitor, AstraZeneca's Crestor and Merck & Co's Zocor.

Statins have been shown to significantly reduce the risk of heart attack and heart disease, and the FDA said the new information should not scare people into stopping taking the drugs.

"The value of statins in preventing heart disease has been clearly established," Amy Egan, deputy director for safety in FDA's Division of Metabolism and Endocrinology Products, said in a statement. "Their benefit is indisputable, but they need to be taken with care and knowledge of their side effects."

Lipitor, which became available late last year in generic form as atorvastatin, is the world's all-time biggest selling prescription medicine with cumulative sales of over $130 billion.

The generic version of Zocor, simvastatin, in 2010 was the second most widely prescribed drug in the United States, according to IMS Health.

The FDA said it was aware of studies in which some patients taking statins may have a small increased risk of higher blood sugar levels and of being diagnosed with type 2 diabetes.

The statin labels will also now reflect reports of certain cognitive effects such as memory loss and confusion experienced by some patients taking the drugs, the agency said. It said those reports generally have not been serious and the symptoms were reversed by stopping use of the statin.

One safety warning long associated with the class of medicines will be reversed, the FDA said: Patients taking statins will no longer need routine periodic monitoring of liver enzymes.

"FDA has concluded that serious liver injury with statins is rare and unpredictable in individual patients, and that routine periodic monitoring of liver enzymes does not appear to be effective in detecting or preventing this rare side effect," it said.

Other statins, most of which are available as generics, include Livalo, Mevacor, Pravachol, Altoprev and Lescol. There are also combination medicines that include statins, such as Merck's Vytorin and Abbott Laboratories' Simcor.

The agency also said Merck's Mevacor, the world's first approved statin, known generically as lovastatin, should never be taken with certain drugs used to treat HIV and certain bacterial and fungal infections due to increased risk of a serious muscle disease.

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